I was using excel-export:0.2.1 plug-in for export data in grail,it was work properly but facing some problem whenever I was Exporting String type of data that was work properly but whenever I was using number(Date and Time),its also work properly but append the single quote along with number which was showing in formula bar in excel sheet which was exporting from the server for fixing this problem I used Apache POI plug-in and formating cell of excel its was working properly.

For formating the cell You can use this code:

XSSFCellStyle cellStyle  = workBook.createCellStyle();          
XSSFDataFormat format = workBook.createDataFormat();
cellStyle.setDataFormat(format.getFormat("m/d/yy h:mm"));
dataCell.setCellStyle(cellStyle);
dataCell.setCellType(Cell.CELL_TYPE_NUMERIC);
dataCell.setCellValue(new Date(1338878999635));

From this code You can formatting the cell 😛